One of the reasons I have a lot of duplicates is because I have a lot of "mixed tape" folders...favorite playlists of mine that I might make every six months or so. I make a new folder with new hard copies of the playlists so that I can burn them to CD or put them on a new hard drive with just a click and drag. Because of this, I have some songs duplicated 5 or 6 times on the same hard drive. That's OK with me and I want to keep it that way. Space isn't the issue. I just don't wany iTunes throwing all those duplicates into the same album. This is one of the reasons why I wanted to fix my folder structure - because then I wouldn't have to worry about iTunes messing everything up.

So what you are saying is that you have a continous mix with the songs that are already broken down into individual tracks. You don't want these individual songs from the mixes to be part of the original mix album.

If this is correct, then click on a song in itunes, click "Info" (Command +I), clear the blocks for Track Number and untick the block for "part of a compilation".